1. Field of the Invention
The present invention relates generally to a punching apparatus to be incorporated into presses for punching sheet metals and other sheet materials and pertains more particularly to a multiple tool holding punching apparatus which can hold various tools, both large and small.
2. Description of the Prior Art
Punching holes in sheet metals and other sheet materials has long been carried out by presses by means of a tool holder which holds a punch or upper tool and a die or lower tool and is mounted on the table of a press beneath the ram thereof. Such a tool holder can hold a certain range of punches and dies for punching holes varying in diameter, since the punches and dies for a certain range of holes are so designed that their body portions to be held by the tool holder are all the same in diameter even if their punching bits or edges are different in size and shape to punch various holes. However, since punches and dies for punching larger holes have to be made larger in diameter, it has been customary to provide two ranges of punches and dies, one of which is used for punching smaller holes varying for example from 1/32 to 11/4 inches in diameter and the other of which is for punching larger holes varying for example from 11/4 to 31/2 inches in diameter, and the tool holder has been designed to carry only one of these set ranges of tools.
Accordingly, it has been a serious disadvantage with the conventional punching apparatus that two tool holders, a small one and a larger one, are required to punch a wide range of holes which are both small and large in size. Therefore, when it is desired to punch holes of the larger range of sizes, it is necessary to remove the whole tool holder from the punching machine and replace it with another tool holder which is adapted to hold the larger tools. This job has been very troublesome and time-consuming and also dangerous since the tool holder is quite heavy and is to be mounted on the high table of the press.
Although there have been some means to overcome the above-mentioned disadvantages, they have been costly, and also it has been very often required to make a wholly special machine in order to incorporate such a means.